1. Field of the Invention
This invention relates to the design, coding, and maintenance of object-oriented applications in computer systems and, more particularly, to efficient use of memory for, caching of, and garbage collection of classes in computer systems.
2. Description of the Related Art
In object-oriented programming, such as programming in the Java® programming language, it is increasingly common to make classes and their instances (objects) immutable. A class in object-oriented programming may be referred to herein as immutable if the state of an instance of the class does not change over its lifetime. The use of immutable classes provides a number of potential advantages in the design, coding, and maintenance of multi-threaded applications. For example, multiple threads may share instances of immutable classes in a safe manner because none of the sharing threads change the immutable object's state. In many applications, a significant percentage of classes are immutable. For example, in many Java®-based applications, instances of the java.lang.string class account for a significant fraction of the heap. Each string contains exactly one character array, which consists of immutable character objects. Character arrays and strings together may account for a very high percentage of the objects in a system.
It may be desirable to reduce the number of objects in a heap to minimize storage requirements. It may also be desirable to reduce the number of objects to be managed so that garbage collection may be performed more efficiently. These and any other improvements in efficiency in handling immutable classes may have a desirable effect on performance of virtual machines, such as are found in Java®-based systems as well as systems that use statically compiled classes. In view of the above, what is needed are improvements to the uses of immutable classes of objects.